In solid state lighting (SSL) applications, a circuit is generally powered by a main line voltage. Therefore, a power converter between the main line voltage as a power source and the load is commonly required to satisfy the following specifications: (1) a power factor correction is required so as to ensure the power factor of the circuit close to 1 and to enable the harmonics to satisfy a local standard limit; (2) a current through the load (e.g., a string of light emitting diodes (LEDs)) should be a stable direct current (DC); (3) the output is protected from being short-circuit so as to ensure safe operation of the load; and (4) the output is optionally galvanically isolated.
Currently, the power converter satisfying the constant current output characteristics and including active power factor correction is generally designed as a two-stage structure, converters at the two stages having different functions respectively. However, in the relate art, since more switch devices and switch driving circuits are required for such a two-stage circuit arrangement, complexity and cost of the circuit are greatly increased.